The process of undercoating a chip significantly increases the reliability of the chip when mounted to a printed wiring board interconnected substrate. Conventional techniques for applying undercoat material include dispensing the undercoat material after the electrical interconnection is made between the chip and the substrate. The dispensed undercoat is then cured in a separate process step.
Chip attach methods using C4 solder ball technology are well known in the art. Using conventional techniques, chips with C4 solder balls are aligned with a relief area (dimple, cavity, or the like) or connection pads on a substrate and pressed into place.
The techniques used for sealing the chips attached to the substrate include injecting sealant material around the periphery of the chip/substrate interface or completely coating the chip and the substrate assembly with sealing material, as well as allowing sealant to flow between the substrate and chip, around the solder balls. Injecting sealant around the periphery does not provide a continuous layer of sealing material and leaves some C4 joints exposed under the chip.
One known method of applying undercoat material to a chip prior to electrical interconnection is disclosed in U.S. Pat. No. 5,279,711 ('711). The '711 reference discloses a method of simultaneously forming a C4 solder connection and sealing the chip/substrate electrical interface utilizing a thin thermoplastic or thermoset material bonded to the top of the substrate prior to the attachment of a chip.
However, the '711 reference discloses a method of attaching and sealing a chip and a substrate in which the substrate includes cavities of a diameter and depth that take into account the statistical variance in the dimensions of C4 solder balls. The method of applying the layer of sealing material to the substrate includes offset printing techniques using a master template having projections with dimensions such that the sealant/adhesive material is applied on the substrate surface while bridging the cavities where the sealant/adhesive materials must not be applied. The material, therefore, is applied on the substrate where the cavities are not located.
The known prior art fails to disclose a method of applying a sealant/adhesive material to a chip prior to electrical interconnection with a substrate which does not require definition of the adhesive surface prior to applying the material to the chip or substrate. In addition, the known prior art fails to disclose a method of applying a sealant/adhesive material to a chip not having C4 solder balls prior to electrical interconnection with a substrate.
Therefore, a need exists for a method and system of applying adhesive/sealant material to a chip or substrate prior to the electrical interconnection therebetween which is quick, reliable, less expensive, and conducive to high volume electronics manufacture in a wide variety of chip/substrate applications.